Among wheel loaders there are wheel loaders mounted with what is called HST (Hydro Static Transmission). In an HST type wheel loader an engine drives a hydraulic pump and a traveling hydraulic motor is driven by hydraulic fluid discharged from a hydraulic pump. This is how the wheel loader is made to travel. In an HST type wheel loader speed and tractive force can be controlled by controlling engine rotation speed, displacement of the hydraulic pump and displacement of the hydraulic motor for driving the wheel loader. (Japanese Unexamined Patent Publication No. 2008-144942).
The operator of such a wheel loader can implement tractive force control selectively. Tractive force may for example, limit displacement of a traveling hydraulic motor to an upper limit displacement less than maximum displacement, thereby reducing maximum tractive force. The operator may choose to implement tractive force control if slip or stall phenomena occur due to excessive tractive force. Doing so reduces maximum tractive force suppressing the occurrence of phenomena such as slip or stall and the like